1. Field of the Invention
The present invention relates to an inductive radio cable used for mobile radio communication carried out on a road, on a railway, in a tunnel, or the like.
2. Background Art
FIG. 1 shows a conventionally known inductive radio cable. In the drawing, a core 1 is made of a magnetic material or an insulator and is successively covered by an inner conductor 2, an insulator 3, an outer conductor 4 and a sheath 5. The inner and outer conductors 2 and 4 are formed by spirally winding conductors on the outer peripheries of the core 1 and the insulator 3 respectively, the inner conductor 2 being wound in the direction opposite to the outer conductor 4.
A current flowing between the inner and outer conductors is inductively radiated into a space outside the inductive radio cable, so that the radiation can be received by an antenna on a moving vehicle.
In the thus described inductive radio cable, however, transmission loss is so large that there is such a problem that a complete inductive radio system becomes expensive because it requires a number of repeaters when the inductive radio cable extends over a long distance.